1. Field of the Invention
The present invention relates generally to optical switches and, more specifically, to an optical switch having an array of movable microelectromechanical reflectors.
2. Description of the Related Art
To achieve high data rates, optical switches are used in many conventional optical fiber communication networks. An optical switch can have a crossbar configuration, in which any selected one of a bundle of input fibers can be coupled to any selected one of a bundle of output fibers.
In some optical switches, the fibers themselves are mechanically moved to switch the optical path between input and output fibers. Such switches suffer from precision and repeatability alignment problems. Slight misalignment between the selected input and output fibers can cause unacceptable signal power loss at the interface. The mechanisms that are required are complex, uneconomical and have slow switching speeds, thereby limiting their use in commercial communications networks.
In other optical switches, one or more mirrors or reflectors are moved to switch the optical path between input and output fibers. Actively controlled mirrors can be fabricated using microelectromechanical systems (MEMS) technology. MEMS technology promises to offer low cost, compact optical modules through the use of low-cost cost batch fabrication. The key mechanical components of MEMS-based micro-machined mirrors can be fabricated on silicon chips using well established, very-large-scale integration (VSLI) complementary metal-oxide semiconductor (CMOS) foundry processes. These processes can include photolithography, material deposition, and chemical etching.
While the operating principles of MEMS optical switching devices may appear to be simple, problems exist with conventional MEMS optical switching devices because of the need for precision control of a movable optical element in a high-speed environment. Conventional MEMS optical switching devices lack precise and controlled mirror movement mechanisms. A movable optical element such as a mirror is disclosed in copending U.S. patent application Ser. No. 09/862,958, filed May 22, 2001, entitled xe2x80x9cMethod and System for Ultra-Fast Switching of Optical Signals,xe2x80x9d assigned to the assignee of the present invention and incorporated herein by this reference in its entirety. One advantage of the disclosed optical element is that it can be very precisely positioned. For example, a mirror can be made to move to one of two precisely defined positions in response to an electrical control signal.
It would be desirable to provide a MEMS-based optical switch having precisely controllable reflectors. The present invention addresses this problem and others in the manner described below.
The present invention relates to a spatial light modulator (SLM) that, in one aspect, has electrically controllable microelectromechanical reflectors arranged in a chain-like manner along an axis such that an optical signal propagates by reflection from an input down the chain to an output. A selected reflector can be moved to a selected one of a number of discrete switching positions. The position determines the angle at which the signal is reflected toward the next reflector in the chain. The combination of positions in which the reflectors are oriented is determinative of the angle at which the signal exits the output. In an illustrative embodiment of the invention, reflectors can move about more than one axis. In such an embodiment, the combination of positions in which the reflectors are oriented is determinative of a two-dimensional direction at which the signal exits the output. Thus, the output signal can be directed at a target point in space.
In the illustrated embodiment of the invention, an optical switch includes an output section comprising a number of SLMs with their inputs arranged in an array or other two-dimensional arrangement. Thus, the input of any of the SLMs of the output section can receive an optical signal. Such an optical switch can also include an input section comprising one or more of the same or similar type of SLM. The outputs of the SLMs of the input section of the switch are arranged to optically couple with the inputs of the SLMs of the output section of the switch. Thus, an SLM of the input section can direct a signal in two-dimensional space such that it impinges upon a selected one of the inputs of the SLMs of the output section. In other words, any of the SLMs of the input section can selectably direct a signal to one of the SLMs of the output section. The switch thus optically couples any selected one of the inputs to any selected one of the outputs in a cross-connect or crossbar manner. Any suitable optical elements, such as lenses, mirrors, and the like, can be interposed between the input and output sections to facilitate mechanical construction or for other purposes.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.